Sowell makes a clear and strong case, as usual.
I have one small quibble - it was specifically Hitler’s betrayal of Uncle Joe that made him a “right winger”; up to that point he was fawned over by the left. But Uncle Joe was the major diety in the pantheon of the utopians. Hitler and Il Duce were, at the time, only revered demi-gods, who, much like the Biblical story, rebelled against their great god, Uncle Joe, and were then cast into the pits of hell - as far from the leftist utopian heaven as possible and are now cast as the Leftists’ great satans in their grand, immoral, morality play.
These specifics are not at odds with Sowell’s explanation, I just wish he would clearly point out that it was their love for that pompadoured murderer that finally made the left decry Hitler and his murderous ways - it wasn’t the murdering to which they objected.
Indeed. Neither Hitler or Stalin expected the treaty to last; they were simultaneously finalizing the division of Poland, and in Hitler's case buying time for his military preparations for a two-main-front war.
So Hitler gladly assented to the treaty. In the event, he was able to move against Stalin, breaching the line of detente in Poland, sooner than Stalin could have anticipated; it reportedly left Stalin catatonic with shock for a day or two.
Sort of like the beginning moves of an aerial engagement, where you're able to turn inside your enemy.
As you point out about the American and English Communists, especially those taking their marching orders from Moscow, they turned literally overnight from peace lovers abhoring the idea of war with the Hun, into cheerleaders for war with him.